EUV collectors are disclosed in U.S. Pat. No. 7,075,712 B2; U.S. Pat. No. 7,501,641 B2; US 2006/0176547 A1; US 2006/0120429 A1; U.S. Pat. No. 7,075,713 B2; EP 1 469 349 A1; US 2008/0266650 A1 and WO 2009/095220 A1.